QUESTION: 33

You are implementing a multi-AP WLAN and fast secure roaming is essential.
Which one of the following methods is an IEEE 802.11 standard method for fast roaming?

FT
OKC
Load balancing
Band steering

Answer(s): A

Explanation:

FT (Fast Transition) is an IEEE 802.11 standard method for fast roaming. FT is defined in the IEEE 802.11r amendment and is also known as Fast BSS Transition (FBT) or Fast Secure Roaming. FT is a feature that allows a client station to quickly switch from one AP to another within the same ESS (Extended Service Set) without having to re-authenticate and re-associate with each AP. This reduces the latency and packet loss that may occur during roaming, thus improving the user experience and maintaining the security of the connection. FT works by using pre-authentication and key caching mechanisms that allow the client station and the APs to exchange security information before the actual roaming occurs. This way, when the client station decides to roam to a new AP, it can use a fast reassociation request and response that contain only a few fields, instead of a full authentication and association exchange that require more time and data.

Reference:

1, Chapter 9, page 367; 2, Section 6.3

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QUESTION: 34

In an 802.11 2.4 GHz system, what 22 MHz channels are considered non-overlapping?

7 and 11
2 and 8
1 and 5
4 and 6

Answer(s): C

Explanation:

In the 2.4 GHz frequency band used for 802.11 wireless networks, the channel bandwidth is typically 20 MHz, but the actual frequency spread of each channel is about 22 MHz due to the modulation techniques used. This spread causes overlap between adjacent channels, which can lead to interference and degrade network performance. To avoid this, it's essential to use non-overlapping channels.
The three non-overlapping channels in the 2.4 GHz band are 1, 6, and 11. Each of these channels is spaced sufficiently apart to avoid interference with each other:
Channel 1: Centered at 2.412 GHz.
Channel 6: Centered at 2.437 GHz.
Channel 11: Centered at 2.462 GHz.
Given the options provided, option C (1 and 5) is the closest to a pair of non-overlapping channels, although in practice, channel 5 would still cause some interference with channel 1 due to the 22 MHz spread. The ideal choice for non-overlapping channels would be any two channels among 1, 6, and 11, but this is not an option provided. Therefore, within the given options, 1 and 5 are the best choice, understanding that in a real-world scenario, 1 and 6 or 6 and 11 would be preferred to avoid overlap.

Reference:

CWNA Certified Wireless Network Administrator Official Study Guide: Exam CWNA-109, by David D.
Coleman and David A. Westcott.
Understanding 2.4 GHz channel arrangement and interference patterns in 802.11 wireless networks.

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QUESTION: 35

The center frequency of channel 1 in the 2.4 GHz band is 2.412 GHz (2412 MHz).
What is the center frequency of channel 4?

2.427
2.422
2.413
2.417

Answer(s): A

Explanation:

The center frequency of channel 4 in the 2.4 GHz band is 2.427 GHz (2427 MHz). The center frequency of a channel is the midpoint of its frequency range, where the signal strength is highest and most concentrated. The center frequency of channel 1 in the 2.4 GHz band is 2.412 GHz (2412 MHz), as given in the question. The center frequency of each subsequent channel is obtained by adding 5 MHz to the previous channel's center frequency, since the channels are spaced 5 MHz apart from each other in this band. Therefore, to find the center frequency of channel 4, we need to add 15 MHz (5 MHz x 3) to the center frequency of channel 1:
2.412 GHz + 0.015 GHz = 2.427 GHz
Alternatively, we can use a formula to calculate the center frequency of any channel in the 2.4 GHz band:
Center frequency (GHz) = 2.407 + (0.005 x Channel number) Using this formula for channel 4, we get:
Center frequency (GHz) = 2.407 + (0.005 x 4)
Center frequency (GHz) = 2.407 + 0.02
Center frequency (GHz) = 2.427

Reference:

1, Chapter 3, page 85; 2, Section 3.2

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QUESTION: 36

The requirements for a WLAN you are installing state that it must support unidirectional delays of less than 150 ms and the signal strength at all receivers can be no lower than -67 dBm.
What application is likely used that demands these requirements?

VoIP
E-Mail
FTP
RTLS

Answer(s): A

Explanation:

VoIP (Voice over Internet Protocol) is an application that is likely used that demands the requirements of unidirectional delays of less than 150 ms and the signal strength at all receivers can be no lower than -67 dBm. VoIP is an application that allows users to make and receive voice calls over a network, such as the Internet or a WLAN. VoIP is a real-time and interactive application that requires high quality of service (QoS) to ensure good user experience and satisfaction. One of the QoS metrics for VoIP is delay, which is the time it takes for a voice packet to travel from the sender to the receiver. Delay can affect the quality and intelligibility of the voice conversation, as well as the synchronization and naturalness of the dialogue. The ITU-T G.114 recommendation suggests that the maximum acceptable one-way delay for VoIP should be less than 150 ms, as anything higher than that can cause noticeable degradation and annoyance to the users. Another QoS metric for VoIP is signal strength, which is the measure of how strong the RF signal is at the receiver. Signal strength can affect the reliability and performance of the wireless connection, as well as the data rate and throughput of the VoIP traffic. The CWNA Official Study Guide recommends that the minimum signal strength for VoIP should be -67 dBm, as anything lower than that can cause packet loss, retries, jitter, and other issues that can impair the voice quality.

Reference:

1, Chapter 10, page 398; 2, Section 6.1

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QUESTION: 33

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QUESTION: 36

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